1. Field of the Invention
The present invention relates to a scale fixating device. Specifically, the present invention relates to a device for fixating a scale enabling accuracy of a scale to be maintained when mounting and fixating an elongated scale to an object.
2. Description of Related Art
As a scale in an instrument measuring length (linear encoder), a tape scale formed in a thin tape shape made of glass or a metal is known. (Japanese Patent Laid-open Publication No. 2011-237310, Japanese Patent No. 4,477,442, Japanese Patent Laid-open Publication No. 2013-7718, and Japanese Patent Laid-open Publication No. S63-252213.) The tape scale provides advantages such as easy lengthening, easy transportation, and simple mounting.
When a tape scale is mounted and fixated to an object, tension is applied in a measurement axis direction. For example, a first end of the tape scale is unmovably fixated to the object and a second end of the tape scale is fixated to a sliding member allowing the second end of the tape scale to move relative to the object. In addition, the tension is applied to the sliding member so as to pull the second end of the tape scale. As a result, even in a case where the tape scale is expanded/contracted by a change in temperature, the tape scale maintains straightness. Generally, a guarantee temperature is set from 0° C. to 50° C. and the tension is applied such that the straightness is maintained within this range. For example, when the tape scale is made of a SUS material, there is about 10.5 μm expansion/contraction per 1 meter with a change in temperature of 1° C. In order to absorb the expansion/contraction, when the encoder is installed at a temperature of 20° C., a pull of 250 μm per 1 meter is required.
As described above, the predetermined tension is applied to the tape scale via the sliding member, however, when inspected after some time following the encoder installation, the tension is often changed. In other words, the sliding member is pulled by the predetermined amount (250 μm per 1 meter), however, a position of the sliding member is displaced from an initial installed position when inspected after some time. A user of the encoder does not check if the tension of the tape scale is appropriate or not once the encoder is installed, which may lead to a measurement error.
Displacement does not occur in all cases and although a cause was unknown, was thought to be a difference in ability during encoder installation. The present inventors have carried out extensive studies and succeeded in shedding light on a fundamental cause, as well as devising a countermeasure to achieve the present disclosure.